Abstract
Objective: To evaluate a series of patients with enlarged parietal foramina for associated brain anomalies.
Background: Enlarged parietal foramina are usually considered a benign calvarial defect.
Methods: Ten patients with enlarged parietal foramina were identified. Seven patients were evaluated with neuroimaging: two by cranial CT and five by CT and/or MRI. Three patients who underwent MRI also underwent MR angiography or MR venography.
Results: Six of seven patients had cranial imaging showing a persistent falcine venous sinus. Three of six patients had variations of occipital cortical infolding. One patient had focal encephalomalacia in close proximity to the persistent falcine venous sinus and one had a previously undiagnosed atretic occipital encephalocele.
Conclusion: This constellation of findings suggests that aberrant vascular evolution during fetal development may affect cerebrovascular, brain, or skull development. Individuals with enlarged parietal foramina (>5 mm) warrant imaging of underlying brain parenchyma and vasculature.
Small parietal foramina (1 to 2 mm) are perforations in the skull near the parietal eminence for the passage of emissary veins.1,2 They are considered a normal common variant in the ossification of the parietal bone, and occur unilaterally or bilaterally in 60 to 70% of the population.3-7 Enlarged parietal foramina (ranging from a few millimeters to several centimeters in diameter) occur with a prevalence of 1:15,000 to 1:25,0002,8-11 and are transmitted through autosomal dominant inheritance. Craniofacial and skeletal anomalies, myelomeningoceles, and encephaloceles have rarely been associated with parietal foramina.7 An increased incidence of large foramina has been reported in patients with obesity, hypogenitalism, microphthalmos, and mental retardation.12 These associations, as well as the etiology and functional significance of parietal foramina, remain obscure.
In general, enlarged parietal foramina are considered a benign anomaly with little clinical significance.5,13 The literature lacks reports of underlying brain or cerebral vascular anomalies. We studied 10 patients with enlarged parietal foramina to look for an association between this “benign” anomaly and other underlying intracranial anomalies.
Methods.
The index patient was identified after presenting to the neurology clinic for evaluation of a large skull defect. She subsequently underwent imaging by MRI. The other nine patients were identified by one of two ways: retrospectively or prospectively. The patients identified retrospectively were found by reviewing neurology and neurosurgery clinic charts for patients who had been evaluated for large parietal foramina (four patients) or by reviewing the radiology records for cases of asymptomatic patients who had been imaged for other reasons such as head trauma (three patients). The patients identified prospectively included two parents who consented to the evaluation after being identified as having parietal foramina.
All identified patients were evaluated in clinic by a child neurologist (A.T.R.), who performed general physical and neurologic examinations. All patients had prior imaging. We defined parietal foramina to be enlarged if they were larger than 5 mm in smallest diameter. All patients were asked to undergo cranial MRI, and five patients consented to do so (three children and two adults). Three of these patients also had supplemental vascular imaging (MR angiography or MR venography [MRV]) performed at random.
A review of all cranial imaging studies was conducted by a pediatric radiologist (G.L.H.) at the Children’s Hospital of Alabama. Of these 10 patients, skull radiographs were available in 9, cranial sonography in 1, CT in 3, and MRI in 5. Six of the 10 individuals had imaging in two or more modalities.
Results.
Nine radiographs demonstrated enlarged parietal foramina varying in size from 0.7 to 5.0 cm (figure 1). CT showed the large bony defects in the three patients studied with this modality (figure 2). Six of seven patients studied with either MRI (four individuals) or CT (three individuals) demonstrated a persistent falcine sinus (figure 3). MRV also demonstrated this venous sinus in the three patients who had this imaging study. Three of seven patients showed variations in occipital cortical infolding (figure 4). One parent volunteer had an occult atretic occipital encephalocele (figure 5). The index child had MRI evidence of focal encephalomalacia in close proximity to a persistent falcine sinus (figure 6). In our patient population, one patient with enlarged parietal foramina had normal cerebral and vascular anatomy.
Figure 1. Enlarged parietal foramina. An anteroposterior radiograph (A) demonstrates enlarged parietal foramina in a 6-month-old infant. Note the confluence posteriorly. These defects, approximately 5.5 × 5.5 cm each, never became substantially smaller, and the patient underwent cranioplasty at 5 years of age. (B) The father of this patient was subsequently radiographed. A Townes view demonstrates the variability in size of parietal foramina.
Figure 2. Cranial CT with three-dimensional reconstruction demonstrates enlarged parietal foramina.
Figure 3. Sagittal T1-weighted MRI shows a persistent primitive falcine vein (arrow). Note the absence of a normal straight sinus venous flow void.
Figure 4. Coronal T1-weighted MRI shows small gyri within the medial occipital lobes. The cortex is of normal thickness, which helps to distinguish stenogyria form polymicrogyria.
Figure 5. Sagittal T1-weighted MRI demonstrates cranium bifidum and an atretic occipital encephalocele.
Figure 6. Axial T2-weighted MRI shows a region of right parietal encephalomalacia (thin arrow). Diminished white matter volume is also noted throughout the right hemisphere. This patient developed acute left-side hemiparesis at 18 months. Clinically and radiographically, this event was consistent with a cerebral infarction. Note the flow void of the persistent primitive falcine vein (thick arrow) in close proximity to the focal encephalomalacia.
None of our patients has a known medical syndrome. The index patient had a large palpable parietal convexity skull defect measuring 5.5 × 10 cm on the top of her head. She had increased tone in her left arm and leg with mild hemiparesis that involved her left face, arm, and leg. In retrospect, she had had a clinical stroke 4 years before this evaluation. The remaining seven children all had normal neurologic examinations. Two of the children required cranioplasty to correct major defects that did not close properly during early childhood, leaving large areas of brain unprotected from potential trauma. They had palpable bone plates. Another two of seven are still infants with palpable defects but otherwise normal examinations. The remaining three children were identified incidentally during evaluation of head trauma.
Both parents reported feeling their skull defects as children, and small defects remained palpable. One parent volunteer also had a 2-cm–diameter, hairless, fluctuating soft-tissue mass over the occiput of her head that was extremely painful to touch and caused severe occipital headaches when pressure was applied to the back of her head. This was identified as an atretic occipital encephalocele on imaging. Both parents had otherwise normal general physical and neurologic examinations.
Discussion.
Enlarged parietal foramina, recognized as a clinical entity by Lancisi since 1707, are said to represent an anomaly of ossification of the parietal bone.14 Although the name implies the same clinical entity, some authors believe that enlarged and small parietal foramina represent separate processes.8 Small parietal foramina typically contain emissary or Santorini’s veins.6 These veins connect occipital veins with the superior sagittal sinus as well as an anastomosis between the middle meningeal and occipital arteries.1,8 Small parietal foramina (1 to 2 mm) are thought to represent a persistence of the most lateral aspects of the primitive parietal notch. They are said to occur in 60 to 70% of adults. Enlarged parietal foramina (>5 mm) transmit these veins only variably,6 and no satisfactory explanation for their functional significance has been given.4 Although they correspond in location to small parietal foramina, they are believed to be a developmental anomaly of parietal bone ossification.
Developmentally, enlarged parietal foramina, also known as fenestrae parietales symmetricae, foramina parietalia permagna, giant parietal foramina, or Catlin marks, arise as a single ossification defect involving both parietal bones.1,5,15 This defect is subsequently cleaved into two foramina by parasagittal islands of ossification.5,10 The cleft typically develops after birth, followed by variable reduction in the size of the foramina with somatic growth during early childhood.8,11 Often the larger foramina is confluent. Hereditary occurrence was first reported by Goldsmith in 1922, when he identified five generations of the Catlin family with enlarged parietal foramina.16 Subsequent reports have confirmed an autosomal dominant mode of inheritance.1,5
With the advent of MRI, we are able to look beyond the cranium of these patients and evaluate their cerebral and vascular anatomy. Our patients demonstrated the expected variability in size of enlarged foramina. They also demonstrated an association between enlarged parietal foramina and anomalies of cerebral venous development and cortical infolding, which have not been reported previously. Specifically, we noted the association between enlarged parietal foramina and the persistent primitive falcine venous sinus and associated hypoplasia or atresia of the straight sinus.17,18 Three of our patients with enlarged parietal foramina also showed variations in occipital cortical infolding. We speculate that this constellation of findings may implicate aberrant vascular evolution during fetal development that preserves the persistent falcine sinus and may adversely affect the normal development of the parietal bone and occipital lobes of the brain.
From a practical standpoint, when cranioplasty or other intracranial procedure is indicated for patients with enlarged parietal foramina, knowledge that venous developmental variations occur with a high frequency warrants cerebral vascular imaging before the procedure. For example, Fein and Brinker1 reported excessive bleeding during craniotomy from the prominent vascular pedicle that penetrated the parietal bone defect. In our series, a substantial number of patients (25%) required cranioplasty because of insufficient closure during early childhood. Furthermore, the combination of enlarged parietal foramina and venous developmental anomalies may represent a small, yet real, risk of thrombosis and stroke.
- Received March 16, 1999.
- Accepted November 2, 1999.
Letters: Rapid online correspondence
REQUIREMENTS
You must ensure that your Disclosures have been updated within the previous six months. Please go to our Submission Site to add or update your Disclosure information.
Your co-authors must send a completed Publishing Agreement Form to Neurology Staff (not necessary for the lead/corresponding author as the form below will suffice) before you upload your comment.
If you are responding to a comment that was written about an article you originally authored:
You (and co-authors) do not need to fill out forms or check disclosures as author forms are still valid
and apply to letter.
Submission specifications:
- Submissions must be < 200 words with < 5 references. Reference 1 must be the article on which you are commenting.
- Submissions should not have more than 5 authors. (Exception: original author replies can include all original authors of the article)
- Submit only on articles published within 6 months of issue date.
- Do not be redundant. Read any comments already posted on the article prior to submission.
- Submitted comments are subject to editing and editor review prior to posting.
You May Also be Interested in
Alert Me
Recommended articles
RECANALIZATION AND OBLITERATION OF FALCINE SINUS IN CEREBRAL VENOUS SINUS THROMBOSIS
Pearls & Oy-sters: Cerebral venous sinus thrombosis involving a persistent falcine sinus
Visual symptoms with dural arteriovenous malformations draining into occipital veins
Intracranial hemodynamic relationships in patients with cerebral small vessel disease